Monte Carlo Simulations of Segregation in Pt-Ni Catalyst Nanoparticles

Journal Article · Thu Apr 01 04:00:00 EST 2004 · Journal of Chemical Physics

OSTI ID:834627

Wang, Guofeng ^[1]; Van Hove, Michel A; Ross, Philip N; Baskes, M I

---

1. LBNL Library

We have investigated the segregation of Pt atoms in the surfaces of Pt-Ni nanoparticles, using Modified Embedded Atom Model potentials and the Monte Carlo method. The nanoparticles are assumed to have disordered fcc configurations at two fixed overall concentrations (50 at. percent Pt and 75 at. percent Pt). We use four kinds of nanoparticle shapes [cube, tetrahedron, octahedron, and cubo-octahedron] terminated by {l_brace}111{r_brace} and {l_brace}100{r_brace} facets to examine the extent of the Pt segregation to the nanoparticle surfaces and determine the equilibrium structures of Pt-Ni nanoparticles at T=600 K. The model particles contain between 560 and 4631 atoms (particle size ranging from 2.5 to 5 nm). Our results imply that a complete (100)-facet reconstruction could make the cubo-octahendral Pt-Ni nanoparticles most energetically favorable, consistent with experimental observations. We predict that at 600 K due to segregation the equilibrium Pt50Ni50 nanoparticles with fewer than 2000 atoms and Pt75Ni25 nano particles with fewer than 4000 atoms would achieve a surface-sandwich structure, in which the Pt atoms are enriched in the outermost and third atomic shells while the Ni atoms are enriched in the second atomic shell. We also find that due to an order-disorder transition the Pt50Ni50 cubo-octahedral nanoparticles containing more than 2000 atoms would form a core-shell structure with a Pt-enriched surface and a Pt-deficient homogeneous core.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic Energy Sciences. Materials Science and Engineering Division, Los Alamos National Laboratory Contract W-7405-ENG-36 (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 834627
• Report Number(s): LBNL--52498
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Vol. 12
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOMS
CATALYSTS
ELECTRONIC STRUCTURE
MONTE CARLO METHOD
PT-NI ALLOY CATALYSIS NANOPARTICLES
SEGREGATION